[PATCH] arch, passt: Use executable link to form AVX2 binary path

[Stefano Brivio <sbrivio@redhat.com>]

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...instead of argv[0], which might or might not contain a valid path
to the executable itself. Instead of mangling argv[0], use the same
link to find out if we're already running the AVX2 build where
supported.

Alternatively, we could use execvpe(), but that might result in
running a different installed version, in case e.g. the set of
binaries is present in both /usr/bin and /usr/local/bin, with both
being in $PATH.

Reported-by: Wenli Quan <wquan(a)redhat.com>
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2101310
Signed-off-by: Stefano Brivio <sbrivio(a)redhat.com>
---
 arch.c  | 25 +++++++++++++++----------
 passt.c |  9 ++++++---
 2 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/arch.c b/arch.c
index ae21d59..71feda3 100644
--- a/arch.c
+++ b/arch.c
@@ -14,26 +14,31 @@
 
 #include <limits.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 
 /**
- * arch_avx2_exec() - Run AVX2 build if supported, drop suffix from argv[0]
+ * arch_avx2_exec() - Switch to AVX2 build if supported
  * @argv:	Arguments from command line
  */
 #ifdef __x86_64__
-static char avx2_path[PATH_MAX];
-
 void arch_avx2_exec(char **argv)
 {
-	char *p = strstr(argv[0], ".avx2");
+	char exe[PATH_MAX], new_path[PATH_MAX + sizeof(".avx2")], *p;
+
+	if (readlink("/proc/self/exe", exe, PATH_MAX) < 0) {
+		perror("readlink /proc/self/exe");
+		exit(EXIT_FAILURE);
+	}
+
+	p = strstr(exe, ".avx2");
+	if (p && strlen(p) == strlen(".avx2"))
+		return;
 
-	if (p) {
-		*p = 0;
-	} else if (__builtin_cpu_supports("avx2")) {
-		snprintf(avx2_path, PATH_MAX, "%s.avx2", argv[0]);
-		argv[0] = avx2_path;
-		execve(avx2_path, argv, environ);
+	if (__builtin_cpu_supports("avx2")) {
+		snprintf(new_path, PATH_MAX + sizeof(".avx2"), "%s.avx2", exe);
+		execve(new_path, argv, environ);
 		perror("Can't run AVX2 build, using non-AVX2 version");
 	}
 }
diff --git a/passt.c b/passt.c
index dd0229a..56fcf5f 100644
--- a/passt.c
+++ b/passt.c
@@ -35,6 +35,7 @@
 #include <sys/mount.h>
 #include <netinet/ip.h>
 #include <net/ethernet.h>
+#include <libgen.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <net/if.h>
@@ -283,11 +284,11 @@ int main(int argc, char **argv)
 {
 	int nfds, i, devnull_fd = -1, pidfile_fd = -1, quit_fd;
 	struct epoll_event events[EPOLL_EVENTS];
+	char *log_name, argv0[PATH_MAX], *name;
 	struct ctx c = { 0 };
 	struct rlimit limit;
 	struct timespec now;
 	struct sigaction sa;
-	char *log_name;
 
 	arch_avx2_exec(argv);
 
@@ -304,14 +305,16 @@ int main(int argc, char **argv)
 	if (argc < 1)
 		exit(EXIT_FAILURE);
 
-	if (strstr(argv[0], "pasta")) {
+	strncpy(argv0, argv[0], PATH_MAX - 1);
+	name = basename(argv0);
+	if (strstr(name, "pasta")) {
 		sa.sa_handler = pasta_child_handler;
 		sigaction(SIGCHLD, &sa, NULL);
 		signal(SIGPIPE, SIG_IGN);
 
 		c.mode = MODE_PASTA;
 		log_name = "pasta";
-	} else if (strstr(argv[0], "passt")) {
+	} else if (strstr(name, "passt")) {
 		c.mode = MODE_PASST;
 		log_name = "passt";
 	} else {
-- 
@@ -35,6 +35,7 @@
 #include <sys/mount.h>
 #include <netinet/ip.h>
 #include <net/ethernet.h>
+#include <libgen.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <net/if.h>
@@ -283,11 +284,11 @@ int main(int argc, char **argv)
 {
 	int nfds, i, devnull_fd = -1, pidfile_fd = -1, quit_fd;
 	struct epoll_event events[EPOLL_EVENTS];
+	char *log_name, argv0[PATH_MAX], *name;
 	struct ctx c = { 0 };
 	struct rlimit limit;
 	struct timespec now;
 	struct sigaction sa;
-	char *log_name;
 
 	arch_avx2_exec(argv);
 
@@ -304,14 +305,16 @@ int main(int argc, char **argv)
 	if (argc < 1)
 		exit(EXIT_FAILURE);
 
-	if (strstr(argv[0], "pasta")) {
+	strncpy(argv0, argv[0], PATH_MAX - 1);
+	name = basename(argv0);
+	if (strstr(name, "pasta")) {
 		sa.sa_handler = pasta_child_handler;
 		sigaction(SIGCHLD, &sa, NULL);
 		signal(SIGPIPE, SIG_IGN);
 
 		c.mode = MODE_PASTA;
 		log_name = "pasta";
-	} else if (strstr(argv[0], "passt")) {
+	} else if (strstr(name, "passt")) {
 		c.mode = MODE_PASST;
 		log_name = "passt";
 	} else {
-- 
2.35.1